Solid state imaging devices, also known as imagers, have been used in various photo-imaging applications, including cameras, camera mobile telephones, video telephones, computer input devices, scanners, machine vision systems, vehicle navigation systems, surveillance systems, auto focus systems, star trackers, motion detector systems, and image stabilization systems among other applications.
There are a number of different types of semiconductor-based imaging devices, including charge coupled devices (CCDs), photodiode arrays, charge injection devices (CIDs), hybrid focal plane arrays, complementary metal oxide semiconductor (CMOS) imaging devices, and other imaging devices. When used with appropriate imaging circuits, imaging devices can capture, process, store, and display images for various purposes.
Imaging devices are typically formed with an array of pixels each containing a photosensor, such as a photogate, phototransistor, photoconductor, or photodiode. The photosensor in each pixel absorbs incident radiation of a particular wavelength (e.g., optical photons or x-rays) and produces an electrical signal corresponding to the intensity of light impinging on that pixel when an optical image is focused on the pixel array. For example, the magnitude of the electrical signal produced by each pixel can be proportional to the amount of incident light captured. The electrical signals from all the pixels are then processed to provide information about the captured optical image for storage, printing, display, or other usage.
Imaging devices can be constructed so that incident light impinges on the frontside or alternatively the backside of the imaging devices. For example, a backside illuminated imaging device receives incident radiation through a backside of the device substrate, over which the imaging device circuitry is formed. In a backside illuminated imaging device, the device substrate is typically thinned so that the photosensors can more easily detect light received from the backside of the imaging device, thereby reducing electronic and/or optical crosstalk. When a backside illuminated imaging device is used to detect incident light having different wavelength components, such as in the case of a color imaging device, the thinned device substrate may not provide sufficient depth for radiation components of longer wavelengths (e.g., red light). Consequently, such longer wavelength radiation components may penetrate through the device substrate without being detected by the corresponding photosensors, thereby compromising quantum efficiency of the imaging device and causing other problems such as crosstalk.
Accordingly, it is desirable to provide an improved structure for a backside illuminated image pixel cell, image pixel array, imaging device, and/or system that reduces the effects of the above discussed deficiencies. It is also desirable to provide a method of fabricating an image pixel cell, image pixel array, imaging device, and/or system exhibiting these improvements.